Cryosurgery, or cryoablation, is one of the oldest of the local thermal ablation techniques. It was initially developed in the 19th century. It has been used for destroying and controlling tissue, such as tumors, deep within the body.
The use of cryosurgical probes for cryosurgery, or cryoablation, has been described in many clinical reports for the treatment of a variety of different benign and malignant tumors. In addition the use of the cryosurgical probes for cryosurgery, or cryoablation, has been described in laparscopic and percutaneous clinical reports.
A summary of the general history of cryosurgery and the mechanism involved therein is well set out in an article entitled “Cryosurgery,” by Boris Rubinsky published in the Annual Reviews in Biomedical Engineering, 2000, 2:157-187, which is incorporated herein by reference.
Cryosurgery, or cryoablation, is a method of in situ freezing of tissues in which subfreezing temperatures are delivered through penetrating, or surface, cryoprobes in which a cryogen, or coolant agent or material, is circulated. The cryosurgical probe quickly freezes tissue adjacent the cryoprobe in order to cause cryonecrosis or tissue death. Irreversible tissue destruction generally occurs at temperatures below −20° C. and cell death is caused by direct freezing, cell membrane rupture, cell dehydration, denaturation of cellular proteins, and ischemic hypoxia. The necrotic tissue then is absorbed or expelled by the body. Multiple applications of freezing and thawing may be applied before the cryoprobes are removed.
This method of cryosurgery has a number of fundamental drawbacks. Presently, cryosurgery, or cryoablation, is primarily an open surgical technique. Depending on the tumor size, one to eight cryoprobes, ranging in diameter from 1.5-8 millimeters in size, are placed in the target tissue. A cryogenic material, typically liquid nitrogen or argon gas, is circulated through the cryoprobes for several minutes in order to achieve temperatures below −120° C. After a second freeze, the cryoprobes are heated, typically by circulating warming fluid or helium gas, and removed and the tracts are packed for hemostasis. Bleeding is often a common complication reported after the cryoablative or cryosurgical procedure. Additional complications include fever, renal failure, sepsis, disseminated intravascular coagulation, and leukocytosis. Other limiting factors include large cryoprobe sizes, damage to the tissue directly adjacent to the cryozone or iceball, and the size and the shape of the iceballs formed in the tissue.
For example, the use of cryosurgical probes for the use in cryosurgery or ryoablation of the prostate described in Onik and Cohen, “Transrectal Ultrasound Percutaneous Radial Cryosurgical Ablation of the Prostate,” Cancer 72:1291, 1993, details the cryosurgical or cryoablative procedure. The cryocoolers or cryoprobes are placed into the prostate gland through cannulas that were previously placed using ultrasound guidance. The irregular shape of the enlarged prostate gland requires a specific iceball shape in order to treat the tissue completely. In order to prevent neighboring tissues or structures from being damaged, the urethra, external sphincter, and the bladder neck sphincter are protected from freezing by a continuous infusion of warm saline through a catheter placed in the urethra. Additionally, cryosurgery or cryoablation of hepatic metastasis poses a different challenge. Unlike primary hepatic tumors, for example hepatocellular carcinoma, the shapes of hepatic metastasis are irregular and typically are in poor locations whereby adjacent tissue or structure damage is a major concern.
The aforementioned difficulties in treating a variety of different benign or malignant tissues and the complications associated with current cryosurgical probes and cryoablative procedures has brought about the need for improved cryosurgical devices and methods.